You don't show us where the string is initialized.

If you have the string verbatim in your editor, you might want to save the file with the UTF-8 encoding and then use utf8; at the top. Personally, I prefer to use charnames ':full'; and then write the characters using \N{...} named escapes.

As for the replacement target, you also need to tell/show us where you get it from, and you need to tell Perl what encoding the string is in. Maybe/most likely, the string already is UTF-8 but Perl doesn't know it. Then you should tell it to Perl by using:

use Encode 'decode';

...

my $string = decode('UTF-8', $input_string);

# Keep only what we want:
$string =~ m!([a-zA-Z0-9]+)!
    or warn "Invalid/empty username in '$string'";
my $real_user = $1;

# Remove stuff we don't want, especially the writing direction isolate
+s:
$string =~ s!\x{2066}|\x{2069}!!g;
[download]